1. Field of the Invention
The present invention relates to supercritical/high pressure fluid processing. More particularly, it relates an apparatus and method for processing work pieces in a supercritical fluid or high pressure liquid environment in a time efficient manner.
2. Prior Art
In the field of microelectronics, semiconductor products such as integrated circuits often undergo processing (for example cleaning) in a supercritical fluid or high pressure liquid, such as, for example carbon dioxide or a mixture of carbon dioxide and a co-solvent. It is necessary for the fluid to be maintained at a controlled pressure and temperature to optimize the process.
Processing of work pieces occurs in a high pressure processing chamber, which must be loaded with the work pieces. One of the major inhibitors to incorporating supercritical fluid or high pressure liquid processing into manufacturing is the low throughput due to long cycle times necessary to pressurize and depressurize the chamber in order to load and discharge the work pieces. Currently, in order to process workpieces in a supercritical fluid (SCF)/high pressure liquid tool, the workpieces must be loaded into the process chamber at ambient temperature and pressure, the tool sealed and then the system must be pressurized by purging the atmospheric air with high pressure fluid which will be brought up to critical processing pressures by pumping on the entire system.
It is an object of the invention to provide a method and an apparatus for increasing throughput in high pressure fluid processing operations.
The invention is directed to a method for operating a system having a processing chamber for performing an operation at high pressures on an object placed in the chamber. The method comprises storing in a storage chamber a quantity of the fluid at a pressure higher than a pressure at which the operation is to take place, while the processing chamber is depressurized to allow reception of a new object; sealing the processing chamber; and allowing fluid stored in the storage chamber to pass to said processing chamber to re-pressurize the processing chamber before performing the operation. The method may further comprise selecting a pressure to which the storage vessel is pressurized based on relative sizes of the storage vessel and the processing chamber.
The method may further comprise purging the process chamber with the fluid before re-pressurizing the processing chamber. It may also further comprise venting the processing chamber after the operation is performed.
The invention is also directed to an apparatus for processing an object with fluid from a fluid source at high pressure. The apparatus comprises a storage vessel for storing a quantity of the fluid supplied from the fluid source; a pump for pumping the fluid from the fluid source to the storage vessel, the pump having an input connected to the fluid source and an output connected to the storage vessel; a processing chamber in which objects to be processed are placed for processing and from which the objects are removed after processing; a first valve between the pump and the storage vessel; a second valve between the storage vessel and the processing chamber; and an exhaust valve associated with the processing chamber to permit the processing chamber to be vented.
The apparatus may further comprises a bypass for bypassing fluid from the output of the pump to the processing chamber.
The first valve may be a two way valve having an input, a first output and a second output, the input being connected to the output of the pump, and a first output connected to the storage vessel, and the second valve may be a two way valve having an output, a first input and a second input, the first input being connected to the storage vessel, and the output connected to the processing chamber; further comprising a bypass connection between the second output of the first valve and the second input of the second valve. In general, the storage vessel has a larger volume than the processing chamber. The storage vessel is pressurized to a higher pressure than the processing chamber. The storage vessel and the processing chamber are relatively sized, and the processing chamber is pressurized, so that when the second valve is opened and pressure equilibrates between the storage vessel and the processing chamber, the processing chamber is at an operating pressure for performing operations on the objects. The fluid source for the apparatus may be a pressured fluid cylinder or a fluid generator. The apparatus may further comprise a heater for heating fluid stored in the storage vessel and a heater for heating fluid in the processing chamber. The pump may be an air driven liquid pump.
The fluid may be a supercritical fluid, such as supercritical carbon dioxide and may include a co-solvent. Operations may be performed at a pressure of between approximately 700 and 6000 psi (48 to 408 atmospheres).